The monitoring of the fetus is a vital aspect of modern labour management. Assessment of the fetal heart rate is a mainstay of such monitoring and can be done externally or by internal electrodes. In certain circumstances, internal monitoring is preferred and provides a more accurate representation of the fetal heart rate pattern for analysis. Internal monitoring probes are usually made of arcuate or spiral metal needles which perforate the scalp skin and are thus secured to obtain electrical signals from the fetal heart. Such probes can be considered invasive to the fetus.
Alternatively, intrauterine probes have been designed which do not have to perforate the fetal skin and which have contact electrodes that lie apposed to the surface of the fetal body and scalp. Reference is directed for example to U.S. Pat. No. 3,326,207 and GB-A-2,195,877. These probes are long and have several built-in electrodes to ensure that at least one of them is in sufficient contact with the fetal skin to obtain an adequate signal. Another sensor, some distance away, is used as a reference electrode. Unless already ruptured spontaneously, the membranes of the amniotic sac have to be ruptured artificially before such a probe is inserted. Because of this aspect and its overall length, such probes can be considered invasive to the mother and the uterine environment of the fetus.
The probe disclosed in GB-A-2,195,877 comprises an elongate flexible strip having a series of protruding electrodes. The strip is of sufficient length (approximately 50 cm) to extend past the fetal head and along the trunk of the fetus. U.S. Pat. No. 3,328,207, issued in 1967, proposed a fetal probe having two inflatable balloons positioned as to contact the shoulder and hip/thigh regions of the fetus, respectively. Each balloon is spherical and carries six or so equatorially spaced electrodes. Additionally, each electrode is provided with a port for the local discharge of a conductive solution. The construction and operation of this probe is considered to be far too elaborate and cumbersome for practical application.